The hydraulic cylinder is a component which is widely used in the construction machinery, and during operations, a piston is required to perform reciprocating movement continuously. When a piston rod extends to a limit position, a piston end face gives a great impact to an end cap, which may cause damages to the hydraulic cylinder. Therefore, a buffer device is required to be provided at that position in order to avoid the damages to the hydraulic cylinder caused by the above impact.
There are great differences between the existing buffer devices due to different application situations and different sizes of the hydraulic cylinders. For small cylinders, compression springs can be employed as buffer devices directly. However, for hydraulic cylinders having a large cylinder diameter and a long stroke, if a compression spring is employed as the buffer device, it is difficult to obtain a spring with sufficient elasticity, and the spring will soon be damaged due to repeated compression. Therefore, for the hydraulic cylinder having a large cylinder diameter and a long stroke, a hydraulic buffering mechanism shown in FIG. 1 is used generally.
Referring to FIG. 1, a buffer device including a big buffer ring 06 and a big buffer sleeve 04 is shown, wherein the big buffer ring 06 is mounted in an intermediate annular groove arranged at a buffering position of a piston rod, and a big buffer sleeve 04 is arranged at the buffering position. A buffer inner hole 07 corresponding to the big buffer sleeve 04 is provided at an opening of the end cap 01 of the rod cavity of the cylinder, and has an inner diameter fitted with the outer diameter of the big buffer sleeve 04. When the piston rod extends out, the big buffer sleeve 04 is firstly inserted into the buffer inner hole 07 to block the oil return passage of the rod cavity in the cylinder barrel 02, and at the same time, a throttle oil channel is formed by a clearance between the big buffer sleeve 04 and the buffer inner hole 07. In this way, the piston 05 can continue to perform movement in the extending direction, but its movement is slowed down due to the damping effect of the throttle oil channel. Further, the closer the piston 05 gets to the end position of the extension movement of the piston rod 03, the longer the throttle oil channel between the big buffer sleeve 04 and the buffer inner hole 07 is, the greater the damping of the throttle oil channel is, the slower the movement of the piston 05 becomes, until the piston rod 03 extends out to reach the end position smoothly.
Currently, the above buffering mechanism is widely used in hydraulic cylinders with a large cylinder diameter and a long stroke to provide a better buffering protection for these hydraulic cylinders.
However, there are obvious defects in the above buffering mechanism. Firstly, the above hydraulic cylinder with a large cylinder diameter and long stroke tends to work in the working conditions of heavy load and high frequency, for example, a drive cylinder used to drive a digging arm of an excavator or the like. In this case, it is required for the big buffer sleeve 04 in the above buffering mechanism to be inserted into the buffer inner hole 07 repeatedly at a high speed. However, the fit clearance between the big buffer sleeve 04 and the buffer inner hole 07 is very small actually, and the piston rod 03 is very heavy, so that the piston rod 03 is likely tilted to one side under gravity. Therefore, the hydraulic cylinder used in the above situation is prone to failure since the buffer sleeve 04 fails to be inserted into the buffer inner hole 07, so that the entire hydraulic cylinder can not operate normally.
Another key problem in the above buffering mechanism is that, the outer diameter of the big buffer sleeve 04 must be precisely fitted with the inner diameter of the buffer inner hole 07, and otherwise the buffering effect may not be achieved. As a result, requirements for the manufacturing precision of the buffering mechanism are extremely high and it is difficult for manufacturers with ordinary production level to meet the requirements. Due to the excessive high requirements of the manufacture precision, the hydraulic cylinders with a large cylinder diameter and a long stroke become a bottleneck problem in producing excavators and other construction machinery, which severely restricts the production capacity of the various manufacturers in the downstream procedures of the production.